drugmakers sprinting to deliver potential covid19 vaccines say theyre facing a new hurdle declining infection rates that could make it hard to test their shotsif the disease ebbs further in some regions not enough people will be exposed to the coronavirus to make studies possible astrazeneca plc chief executive officer pascal soriot said thursday in a briefing with journalists researchers may have to consider deliberately infecting healthy volunteers with the virus though its still too early to take that step he saidalso see coronavirus vaccine status from 30 indian covid19 vaccine candidates to latest developments in modernas vaccine here is everything you need to knowthe problem we all have is we are running against time soriot said we see already in europe the disease is declining its still going in the uk still going in the us but very soon the disease intensity will be low and it will become difficult so we have to move very quicklyastra which is helping scientists at the university of oxford develop a vaccine has joined dozens of companies including sanofi johnson johnson glaxosmithkline plc and pfizer inc working on experimental pandemic shots while lockdowns have helped nations curb infection rates governments need to halt the virus to fully reopen businesses and schoolssome transmission of sarscov2 is key to determining whether vaccines work now researchers are contemplating where and how they can undertake studies with the best chance of successthe disease is now moving to other parts of the world especially countries in the southern hemisphere such as brazil and south africa paul stoffels johnson johnsons chief scientific officer said he and soriot spoke in a video briefing held by the international federation of pharmaceutical manufacturers and associations an industry groupfor the companys planned latestage trials aimed at proving its vaccine is safe and effective hopefully that can be done in the north he said if not well have to go to the southwhile studies in which scientists infect subjects called challenge trials pose significant potential risks they could be considered in dire situations and with certain disclosures and protections the world health organization said earlier this monththe ethical issues around this are yet to be resolved soriot said i suspect maybe at some point it will be done but we feel its too early because we still have a chance to show efficacy in a normal way