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Most COVID-19 vaccinations in the U.S. involve a two dose vaccine.Noam Galai/Getty Images
  • New research shows how important it is to get both doses of the COVID-19 vaccine.
  • A new study showed that vaccine effectiveness rose from 33 percent to between 60 and 88 percent after a second dose, depending on the variant and vaccine type.
  • Experts say these findings are encouraging and that as many people should get vaccinated as possible to stop the virus from reproducing.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub and follow our live updates page for the most recent information on the COVID-19 pandemic.

By now, most of us are very familiar with the new cards issued after receiving our first of a two-dose regimen of the COVID-19 vaccine.

It documents the type of vaccine you received and the date — and it typically has a reminder of when you should get your critical second dose. Yes, you can get the Johnson & Johnson single dose but the vast majority of administered vaccines in the United States have been two-dose regimens.

Recent research confirms that after only one dose of a two-dose vaccine, you’ll only have “a relatively weak immune reaction” against the novel coronavirus.

However, in a more recent study (not yet peer-reviewed), Public Health England (PHE) finds that a second dose does more than shield you from a SARS-CoV-2 infection — it provides powerful protection against coronavirus strains, like the one first detected in India (B.1.617.2).

“We expect the vaccines to be even more effective at preventing hospitalization and death,” said Dr. Mary Ramsay, head of immunization at PHE, in a statement. “So it is vital to get both doses to gain maximum protection against all existing and emerging variants.”

The PHE study analyzed data for all age groups and several ethnicities from April 5, and included a little over 1,000 people confirmed to have an infection with this variant using genomic sequencing.

Importantly, both vaccines were only about 33 percent effective against symptomatic disease from B.1.617.2 and only 50 percent effective against the more common variant first detected in the United Kingdom (B.1.1.7) after a single dose.

However, after two doses, researchers found that the Pfizer vaccine was 88 percent effective against symptomatic disease from the B.1.617.2 variant, and 93 percent effective against the B.1.1.7 variant. These percentages were recorded 2 weeks after the second dose.

They also found that two doses of the AstraZeneca vaccine were 60 percent effective against symptomatic disease from the B.1.617.2 variant and 66 percent effective against the B.1.1.7 variant.

The study authors said the AstraZeneca vaccine’s lower efficacy after two doses, when compared to Pfizer’s, might be because it was mostly given to older people, a group that tends to have weaker immune responses.

“While there is much emerging data to suggest that the first dose conveys some degree of protection, it’s imperative to get both doses,” Dr. Jeremy Levin, chairman and CEO of OVID Therapeutics and chairman of the Biotechnology Innovation Organization (BIO), told Healthline. “The data are unequivocal that the regimen provides over 90-percent protection against COVID-19.”

According to Levin, there are three subtypes of the variant first detected in India, each with a slightly different genetic makeup:

  • B.1.617.1 (the “original” B.1.617)
  • B.1.617.2
  • B.1.617.3

“For example, the B.1.617.2 variant has mutations called 452R and 478K, both linked to increased transmissibility,” said Levin. “No mutation in any of the B.1.617 variant subtypes is associated with increased disease severity.”

Levin added that a U.K. government advisory committee, the Scientific Pandemic Influenza Group on Modelling, said on May 12 that there is a “realistic possibility” that B.1.617.2 is 50-percent more transmissible than B.1.1.7, according to the available data.

“It appears that data show the current vaccines are effective against these variants,” confirmed Levin.

According to Dr. David Hirschwerk, an infectious diseases specialist at Northwell Health in New York, while available vaccines have remained “very effective” against emerging variants, there’s no guarantee that one won’t arise that the vaccines are less able to fight.

His solution to this problem is simple.

“The best way to reduce that likelihood is to limit ongoing viral replication around the entire world,” he said. “We need more people vaccinated everywhere.”

Hirschwerk emphasized that it’s also important for younger people to receive the vaccine.

Because of this, he also mentioned, younger people who are unvaccinated are at higher risk of contracting and transmitting the virus

New research from the United Kingdom shows how important it is to get both doses of a two-dose COVID-19 vaccine — finding that after being fully vaccinated, you’re powerfully protected against infection with SARS-CoV-2 and its currently circulating variants.

Experts say these findings are encouraging and that as many people should get vaccinated as possible to stop the virus from reproducing.

They also say it’s important for all age groups to be vaccinated. This is especially true for younger people as they tend to be much more mobile in the community, presenting a greater risk of virus transmission.