Novavax, a little-known company backed by the U.S. federal government’s Operation Warp Speed, said for the first time Thursday that its Covid-19 vaccine offers robust protection against the virus. However, it was also found that the vaccine was not as effective against the fast-spreading variant, which was first discovered in South Africa. This is yet another setback in the global race to end a pandemic that has killed more than 2.1 million people.

The news was problematic for the United States, which hours earlier reported its first known cases of the contagious variant in two unrelated people in South Carolina. And it came just days after Moderna and Pfizer said their vaccines were less effective against the same variant as well.

Novavax, one of six vaccine candidates supported by Operation Warp Speed ​​last summer, has conducted trials in the UK, South Africa, the US and Mexico. On Thursday, an early analysis of the 15,000-person study in the UK said the two-dose vaccine had an efficacy rate of nearly 90 percent there. In a small study in South Africa, however, the effectiveness rate fell to just under 50 percent. Almost all cases that scientists have analyzed there so far were caused by the variant known as B.1.351. The data also showed that many study participants were infected with the variant even after they had Covid.

“We have the first study – we’re the first to do an efficacy study – in the face of a changing virus,” said Stanley Erck, President and CEO of Novavax. He said the researchers expected the variants to change the test results, but “the extent of the change came as a little surprise to everyone.”

The South African study was relatively small with only 4,400 volunteers and was not intended to provide an accurate estimate of the protection of the vaccine. Still, the results were so impressive that the company announced it would soon be testing a new vaccine tailored to protect against the variant from South Africa. “You have to make new vaccines,” said Mr. Erck.

While Pfizer and Moderna’s vaccines are based on newer mRNA technology that was not used in previous vaccines, Novavax’s candidate uses an older, more established method of injecting coronavirus proteins to trigger an immune response.

The fact that three vaccines all showed decreased efficacy against the South African variant is not encouraging, and the results Novavax announced Thursday were the first to go outside a laboratory testing how well a vaccine did in humans that were infected with a new variant worked. Johnson & Johnson is also close to announcing the results of its Covid-19 vaccine trials and has also tested its candidate in South Africa.

Novavax’s announcement increases stakes for Johnson & Johnson. The company was expected to announce its results earlier this weekend, and the delay has sparked speculation among scientists that the company also found its vaccine did less well in volunteers from South African studies infected with the variant works. In a call for earnings on Tuesday, Alex Gorsky, the company’s chief executive officer, said they look forward to sharing the results of their late-stage results by early next week.

The emergence of several highly contagious variants has hampered efforts to get the pandemic under control and has led world leaders to stop traveling to places like the UK and South Africa, even though the variants appear to have already circled the globe. In the United States, researchers have warned that the variant first identified in the UK, which is believed to be more contagious, could become the dominant form of the virus in that country by March.

The United States lags far behind other countries in testing for such variants, and that of South Africa has been found in about 30 countries.

However, experts have also given reasons for optimism and found the vaccines continue to be effective. The best way to combat contagious new varieties is to continue vaccination and other public health interventions, which slow the virus’ ability to infect and further mutate new people. Drug manufacturers could update their vaccines and offer new ones on a regular basis, similar to the flu vaccine.

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Answers to your vaccine questions

Am I eligible for the Covid vaccine in my state?

Currently more than 150 million people – almost half of the population – can be vaccinated. But each state makes the final decision on who goes first. The country’s 21 million healthcare workers and three million long-term care residents were the first to qualify. In mid-January, federal officials asked all states to open eligibility to anyone over the age of 65 and adults of any age with medical conditions that are at high risk of becoming seriously ill or dying of Covid-19. Adults in the general population are at the end of the line. If federal and state health authorities can remove bottlenecks in the distribution of vaccines, everyone over the age of 16 is eligible as early as spring or early summer. The vaccine has not been approved in children, although studies are ongoing. It can take months before a vaccine is available to anyone under the age of 16. For the latest information on vaccination guidelines in your area, see your state health website

Is the Vaccine Free?

You shouldn’t have to pay anything out of pocket to get the vaccine, despite being asked for insurance information. If you don’t have insurance, you should still get the vaccine for free. Congress passed law this spring banning insurers from applying cost-sharing such as a co-payment or deductible. It consisted of additional safeguards prohibiting pharmacies, doctors, and hospitals from charging patients, including uninsured patients. Even so, health experts fear that patients will end up in loopholes that make them prone to surprise bills. This could be the case for people who are charged a doctor’s visit fee with their vaccine or for Americans who have certain types of health insurance that are not covered by the new regulations. If you received your vaccine from a doctor’s office or emergency clinic, talk to them about possible hidden costs. To make sure you don’t get a surprise invoice, it is best to get your vaccine at a Department of Health vaccination center or local pharmacy as soon as the shots become more widely available.

Can I choose which vaccine to get?How long does the vaccine last? Do I need another next year?

That is to be determined. It is possible that Covid-19 vaccinations will become an annual event just like the flu vaccination. Or the vaccine may last longer than a year. We’ll have to wait and see how durable the protection from the vaccines is. To determine this, researchers will track down vaccinated people to look for “breakthrough cases” – those people who get Covid-19 despite being vaccinated. This is a sign of a weakening of protection and gives researchers an indication of how long the vaccine will last. They will also monitor the levels of antibodies and T cells in the blood of people who have been vaccinated to see if and when a booster shot might be needed. It is conceivable that people might need boosters every few months, once a year, or just every few years. It’s just a matter of waiting for the data.

Does my employer need vaccinations?Where can I find out more?

The Novavax study in the UK tested how many volunteers developed symptoms of Covid-19 a week after receiving a second dose. The company said Thursday that its initial analysis found that of 62 participants who got the disease, 56 had received a placebo and 6 had received the vaccine. According to Novavax, the newer, more contagious variant, first identified in the UK, caused about 50 percent of the cases in the study.

If these results were reflected in the larger clinical trial in the United States and Mexico, which involved approximately 16,000 out of 30,000 people, it would equate the vaccine with the Moderna and Pfizer-BioNTech vaccines, which were shown to be about 95 percent are effective.

But the news in South Africa was not that encouraging. Novavax’s smaller study found the vaccine to have an overall effectiveness of 49.4 percent. (The company reported that about 6 percent of the study participants were HIV positive, and for those who weren’t HIV positive, the vaccine had an effectiveness of 60 percent.) The company said the study was conducted from September through September The recording of cases of Covid-19 began midway through this month when the more contagious variant was widespread. According to Novavax, 44 study participants developed Covid-19 and sequenced the genetic lineage of 27 cases. Of these, 25 cases were caused by the more contagious version of the virus.

The company also said that about a third of study participants in South Africa had previously developed Covid-19 after being infected with the original form of the virus, and that their results showed that these previous infections did not protect them from the new variant. The company said its vaccine offered some protection for those who had previously contracted the disease, but did not include that group in its analysis.

Novavax started work on a new version of the vaccine this month to address more contagious variants that could either be used as a booster or given at the same time as their original vaccine.

The variant B.1.351 was first noticed by scientists in December. It contains a number of mutations, including some that change the shape of the virus’s surface and make vaccines less effective.

Looking back on older samples, South African scientists found the first evidence for B.1.351 from October. But by December, it had swept the country and became the dominant coronavirus line in many regions.

That alone would make B.1.351 a worrying development. In the UK, researchers found another rapidly spreading variant known as B.1.1.7. In Brazil and California, other scientists have found variants that may be more contagious than previous forms of the coronavirus.