In one, researchers from Israel’s largest hospital looked at what happened when more than 7,000 people were vaccinated there. Between their first and second doses of Pfizer / BioNTech vaccine, the number of infected people dropped. By the second to fourth week after the first shot, the percentage of symptomatic infection dropped by 85%.
In a second, Canadian researchers found evidence of more than 90% protection after a single dose of Pfizer / BioNTech vaccine.
It is not at all clear how long this protection would last, and both the Pfizer and Moderna vaccines have been tested and approved based on a two-dose treatment. The companies, the U.S. Food and Drug Administration and top government officials, including the director of the National Institute of Allergy and Infectious Diseases, dr. Anthony Fauci, warned to go outside what was known and tested.
“People need to continue to get their second chance,” White House senior adviser Andy Slavitt told the CNN Chris Cuomo on Thursday night about the Covid-19 response. “The second shot does contribute to their immunity, and what we need to do is go through our first doses in the field faster, but no one advises people to skip their second shot at this point.”
But the US is struggling to get even first doses into the population, and is watching the death toll from the virus gradually rise towards 500,000. While U.S. federal officials initially said they hope someone who wants a vaccine can get it by April, they have now pushed the timeline back to July.
And new variants that seem to make the virus more contagious are appearing around the world and around the country. It is possible that they may trigger a surge in the spread of the virus long before 70% to 85% of the population – the percentage that Fauci estimates are needed to bring about herd immunity – can be vaccinated.
The team looked at the rate of infection for about three weeks before the workers received a second dose of vaccine. They found a 47% decrease in symptomatic coronavirus infections among health workers during the first two weeks after the first shot, and an 85% reduction during the next two weeks.
“Our data show significant early decreases in SARS-CoV-2 infection and symptomatic COVID-19 doses after the first administration of the vaccine,” said Dr. Eyal Leshem and colleagues wrote.
“Early reduction of COVID-19 rates provides support to delay the second dose in countries with vaccine shortages and scarce resources, to enable higher population coverage with a single dose.”
They passed on documents that Pfizer and its partner BioNTech submitted to the FDA when they asked for permission for emergency use last year.
“Even before the second dose, BNT162b2 was extremely effective, with a vaccine efficiency of 92.6%, a finding similar to the first dose efficacy of 92.1% reported for the mRNA-1273 vaccine (Moderna),” write them.
“With such a very protective first dose, the benefits of a rare vaccine can be increased by postponing second doses until all priority group members are offered at least one dose,” they added.
They noted that it is not clear how long protection lasts if people receive only one dose of vaccine. Clinical trials show a major boost in the production of antibodies after the second dose of the Moderna or Pfizer vaccine.
Given the current shortage of vaccines, the postponement of the second dose is a matter of national security which, if ignored, will certainly result in thousands of Covid-19-related hospitalizations and deaths in the United States this winter – hospitalizations and deaths that would be prevented with a first dose of vaccine, ‘they argued.
Dr Tom Frieden, a former director of the US Centers for Disease Control and Prevention, now CEO of the organization Resolve to Save Lives for Health, says there are arguments for and against postponing the second dose until millions of people can be vaccinated.
“Subsequent doses ‘strengthen’ the immune response by activating immune cells created after the first dose to provide stronger, longer-lasting protection,” he added.
“For some COVID-19 vaccines, multiple dose multiplication is an important reason to increase the strength of the antibody response.”
But he also notes that prolonging the time between doses has never been shown to reduce the effectiveness of a vaccine, and in some cases – the HPV vaccine is an example – it boosts the immune response.
“A disadvantage of a longer interval between doses of any type of vaccine, however, is that full protection is unlikely until all doses have been administered. In addition, it is not yet known for mRNA vaccines such as the Pfizer and Modena vaccines. The timing of the second dose is critical to provide a sustained immune response because mRNA vaccines were not used or approved in the late stages before the COVID-19 pandemic, “Frieden noted.
The advent of more transferable variants could change the equation, he said. “Maximizing the number of people with a certain degree of immunity can be especially important if a highly transmissible variant spreads rapidly. Some experts in the US have suggested that the policy be reconsidered to delay second doses in favor of administering a first dose to more people., because highly transmissible varieties of SARS-CoV-2 are distributed in the United States. ‘
But there is another argument. What if the new variants spread among people who are only partially protected by having one dose of vaccine – and even worse variants develop as a result?
“It is not clear how well a single dose of any two-dose COVID-19 vaccine infection can occur with emerging variants,” Frieden noted.
Even single-dose vaccines do not completely solve the dilemma. Johnson & Johnson is seeking FDA approval for its single-dose Covid-19 shot. But it is also testing a two-dose regimen to see if it works better.